Axial-piston pump with control rods



Feb. 24, 1970 K. WINTER AXIAL-PISTON PUMP WITH CONTROL RODS 5Sheets-Sheet 1 Filed Dec. 27. 1967 2 3 0W 8 w d Q 3 t w a wq 5m\\\\\\\\\\\\\ K. WINTER 3,

AXIAL-PISTON PUMP WITH CONTROL RODS Filed Dec. 72.7A 1967 3 Sheets-Sheet2 Klaus Wi'n'rer INVENTOR.

. ATTORNEY 24, 31976 K. WINTER 3,496,873

AXIAL-PISTON PUMP WITH CONTROL Robs Filed Dec. 2?, 1967 s Sheets-Sheet sKlaus Winf'er mvem'on.

BY M

A'I'I'ORNEY Unite States Patent 3,496,873 Patented Feb. 24, 1970 U.S.Cl. 103-37 Claims ABSTRACT OF THE DISCLOSURE An axial-piston pump withswash-plate hydraulic apparatus and a nonrotating cylinder block inwhich a set of pistons reciprocate and cause the circulation of aworking fluid through intake and discharge valves. The length of thepiston stroke and, with it, the capacity of the pump can be controlledmanually or, alternatively,

automatically by utilizing a variable pressure differential via rodsextending into the pistons.

The invention relates to a hydraulic machine and, more particularly, toan axial-piston pump comprisin a reservoir for the fluid medium in whichthe fluid is delivered to an array of pistons concentrically disposedabout a drive shaft and driven in and out of their respective cylindersin a direction parallel to the drive shaft by rotation of a swash-platehydraulic apparatus mounted on the drive shaft at a fixed (or possiblyvariable) angle of tilt relative to the shaft axis.

In prior axial-piston pumps with swash-plate mechanisms the adjustmentof controllable components was often fOund to be uneconomical and liableto introduce complications which offset any advantages to be gained fromthe apparatus. Regulation of the volume and direction of the fluid flowthrough changes in the angle between the swash plate and the pistons,which was designed to control the variable displacement of such pumps,was apt to introduce friction effects in the drive coupling and toaggravate, through accompanyin temperature fluctuations, damage throughwear and tear, inadequate lubrication and insufficient filtra ion.Similar d sadvantages were encountered when the rotating cylinder barrelhad to be axially shifted.

It is an object of my present invention to overcome the disadvantages ofknown axial piston pumps with swash-plate apparatus, and to provide asimple and inexpensive mechanism which is easy to control and tomaintain, and which gives trouble-free service.

A more specific object of my invention is to p ovide an improved axialpiston pump in which a swash plate tilted with respect to the axis ofits supporting drive shaft rotates with respect to non-rotatable pistonsconcentrically disposed about a cylinder block and lon itud nallydisplaces the pistons in their cylinders, the direction of rotationbeing reversible.

Still ano her obiect of th s invention is to rovide an improved systemfor controllin the length of the efl ective piston stroke in order tovary the volume of the displaced hydraulic fluid and through it, theoutput to be deliver d by the axial-piston pump.

These objects and others, which will become apparent hereinafter, areattained, in accordance with the present invention. through control rodsslidably received in respective bores inside the pistons and passingthrough the intake valves which separate the intake chamber from theannular pumping chambers which serve as working spaces for the pistons.The rods, attached at one end to a support plate mounted in the cover ofthe pump housing and terminating in leading edges at their other ends,proximate to the swash plate, alternately block and unblock the thrustexerted upon the compression side of the intake valves by covering 0runcovering, accordin to the desired length of the stroke, orifices whichlead from the piston bore to the pumping chamber. With respect to manualoperation, the support plate for the rods can be longitudinallydisplaced through interaction of a threaded spindle driven by gearmeans. According to another feature of the present invention, thelongitudinal variation of the piston stroke through the control rods iseffected by differential hydraulic action upon two piston surfaces ofdissimilar area.

The above and other objects, features and advantages of my inventionwill become more readily apparent from the following description,reference being made to the accompanying drawin in which:

FIG. 1 is a longitudinal cross-sectional view of a pump according to myinvention;

FIG. 2 is an axial cross-sectional view taken on the line II-II of FIG.1; and

FIG. 3 is a longitudinal cross-sectional view showing alternateadjusting means for the assembly of FIG. 1.

In the drawing there is shown a housing 1.9 which forms a cylinder block19a and is closed at its lefthand and by a cover 20, with a seal 28provided at the junction of these adjoining parts. The hydraulic fluid,e.g. oil, which also serves to lubricate the moving parts of the pump issupplied to the intake compartment 6 via a port 37, from the reservoir(not shown). The compartment 6 is thus formed between the cover 20 andthe cylinder block 19a. The load is supplied with fluid under pressurefrom the outlet fitting 38 which forms part of an outlet means describedin greater detail below. The housing itself is attached by lugs 33 to asupport. Power from a prime or secondary mover is delivered to a driveshaft 1 which is journaled in sealed bearing 26 in a hearing plate 42held in place by a split ring 27. The inner end of drive shaft 1includes a boss 29 which fits accurately for pivotal movement of a swashplate 2. Swash plate 2, tilted at an acute angle relative to the axis ofdrive shaft 1, is rotated about the shaft axis on the shaft. Swash plate2 is rotatably supported by ball bearings 30 having an inner thrust race31 (against which the swash-plate disk 2 applies the axial reactionforce of the pumping action) and outer race 32 resting against plate 42.The ball bearings are centered on the axis of drive shaft 1. A recess35a in the cylinder block 19a beyond the swash plate 2 receives roller(needle) bearings 35 to take up unequal radial forces developed duringrotation of the swash plate in pumping action.

In the cylinder block 19a there are located several tubular pistons 5angularly spaced around the cylinder periphery at uniform intervals, sothat their longitudinal axes are parallel to the axis of drive shaft 1.Each piston, fitted into a cylinder bore 7a, defines therewith a workingspace or pumping chamber 7 and is urged by springs 3 resiliently againsta slidable piston shoe 4, swiveling on the head of the piston; thus eachpiston is driven back and forth in its cylinder as the orbiting swashplate alternately compresses and relieves the springs 3. Fluid from theintake compartment is channeled through a double springloaded intakecheck valve 8 which has the form of a ringplate valve, to the pumpingchambers 7, thence via the outlet check valve 9 and from there to adischarge duct 14 of the outlet means and via chamber 10 to the load.

A bleeder screw 34, threaded into the pump housing, permits venting ofair for priming the pump. Each piston 5 contains in a longitudinal bore5a through its center a compression rod 11 which at one end is firmlyattached by a head 46 to a support plate 15 axially movable on the pumpcover 20 and located in the intake compartment 6.

3 At its other end, proximate to the swash plate, each control rod 11has a leading edge 16 with which it alternately covers and uncovers,with each piston stroke, an orifice 17 which leads radially out of thepiston bore and into a longitudinal channel 25 cut in the form of agroove in the outer piston surface and from there to the annular space7.

The support plate 15 which holds the array of control rods 11 isthreaded onto a spindle sleeve 14 forming the fluid passage or outletduct inside the cover 20. A drive gear 13 is attached to the axiallyfixed rotatable sleeve 14 and meshes with a driving gear 41. When ahandwheel 12 is manually rotated, these gears advance the support plate15 which is screwed onto the sleeve 14 and whereby longitudinallydisplace the control rods 11 attached to the support plate extend intothe pistons 5.

During the suction stroke, while the piston is moving from left to rightas shown in FIG. 1, fluid is drawn through the intake valve 8 and, afterorifice 17 has been unblocked, also through that opening into theinterior of the piston along groove 25, During the compression stroke,while the piston is moving from the right to the left as viewed in FIG.1, fluid from the annular chamber 7 of progressively decreasing volume,is forced through the orifice 17 and through the piston bore a, 5a, 5a"into the swash-plate compartment 45 until the leading edge 16 of thecontrol rod 11 blocks the orifice. At that point the effective portioncompression stroke starts and moves fluid from the annular chamberthrough the compression valve 9 to the compression chamber compartment45 is connected via a passage 45a, 45b with intake compartment 6. Thecompression stroke ends when piston 5 has reached its leftmost position.

Manual adjustment of the control rods in a longitudinal direction, byway of the support plate 15, the handwheel 12 and the gear transmission13 and 41, controls the length of the compression stroke and thereby theoutput of the axial piston pump. An alternate arrangement for theadjustment of the control rods is illustrated in FIG. 3. In contrast tothe preceding system a sleeve 18 forming the fluid passage of the outletduct is longitudinally slidable inside the housing 19. Inside cover 20with its cylindrical extension 46 there is a spindle 21 coaxiallyaligned with the longitudinal axis of the sleeve 18. Part of spindle 21extends into a chamber 48- that is connected with the outlet chamber 10'and is provided with external threads onto which is screwed a hexagonalhead 24. This hexagonal head cooperates with hexagonal recess 48preventing rotation of the head and supports the spring 22. Theknee-shaped support plate 23, which carrier control rods 11 on itsperiphery as in FIG. 1, is attached at its hub to sleeve 18 by twocirclips 47 that hold it in a perpendicular position relative to thelongitudinal axis of the sleeve. A stepped shoulder 49 of the sleeve 18in the intake chamber 6 decreases one differential-piston area 50 of thesleeve 18 relative to an oppositely effective area 51, both of which areunder pressure from the fluid in chamber 10. When springs 22 arerelaxed, as viewed in the drawing, sleeve 18 is moved to the leftbecause its right frontal area offers a greater surface to the pumppressure than does the left frontal area. As soon as the pressure,defined as force per unit area, is equalized between the two frontalareas, tightening of springs 22 holds the sleeve in a certain positionfrom which it is shifted only when another pressure difference builds upbetween the two areas. The greatest displacement to the left which thesleeve 18 can be given corresponds to the distance 52 between thecontrol rods 11 and the pump cover 20.

Through support plate 23 which is attached to the sleeve 18, and thecontrol rods 11 affixed to the support plate, the sleeve motionconstitutes the essential part of a servomechanism in which variationsin the pressure of the pump are automatically compensated for byvariations in the stroke length of the pistons.

I claim:

1. An axial-piston pump comprising:

housing means having an axis and formed with a plurality of axiallyextending cylinders angularly spaced about said axis;

a plurality of pistons respectively received in said cylinders andaxially reciprocable therein while defining with said housing meanspumping chambers of variable volume;

an input shaft rotatably mounted in said housing means and having a headrotatable about said axis and cooperating with said pistons at one endthereof for reciprocating same upon rotation of the shaft, the otherends of said pistons terminating within said cylinders;

intake-valve means communicating with said chambers proximal to saidother ends of said pistons for delivering fluid to said chambers duringan intake stroke of the respective piston enlarging the correspondingchamber;

outlet means in said housing means including a respective check valvecommunicating with each of said chambers proximal to said other ends ofsaid pistons for discharging fluid from said chambers unidirectionallyduring a compression stroke of the respective piston decreasing thevolumes of the corresponding chamber, said pistons being each formedwith an axially extending bore opening at said other ends, an apertureat a location intermediate said ends and communicating between said boreand said chamber, and a vent passage opening into said bore proximal tosaid one end; and

control means for establishing effective portions of the compressionstrokes of said pistons, said control means comprising:

respective axially extending, angularly spaced, mutually parallelcontrol rods each slidably received in a respective one of said boresand extending into the latter through said other end of the respectivepiston for selectively blocking and unblocking the respective apertures,said rods having corresponding extremities projecting from said pistonsat said other ends,

a control body centered on said axis and extending outwardly therefromwhile engaging said extremities of said rods, and

mechanism for axially shifting said body toward and away from said shaftto regulate the point in each stroke of each piston at which the rodobstructs the respective aperture to define the effective piston stroke,thereby confining the fluid within the respective chamber for therespective effective portion of the compression stroke.

2. An axial piston pump as defined in claim 1 wherein said apertures aregenerally radial orifices formed in each piston and communicatingbetween the corresponding piston bore and pump chamber, said controlrods each having a control edge alternately blocking and unblocking therespective orifice during each piston reciprocation, said pistons andsaid cylinders each define an axially extending channel along the outerwall of the respective piston communicating between the respectivepumping channel and the respective radial orifice.

3. An axial piston pump as defined in claim 2 wherein said mechanismincludes an axially fixed spindle rotatably mounted on said housingmeans remote from said head, and means external of said housing meansfor rotating said spindle, said body threadedly engaging said spindleand being nonrotatable for axial advance upon rotation of said spindle,said means for rotating said spindle comprising a driven gear connectedto said spindle, a driving gear rotatably mounted in said housing meansand meshing with said driven gear and a handwheel operable externally ofsaid housing and connected with said driving gear for manually rotatingsame, said spindle being tubular and centered on said axis while formingsaid outlet means.

4. An axial-piston pump as defined in claim 2 wherein said adjustingmeans includes a differential piston axially shiftable in said housingmeans and subjected to the fluid pressure at said outlet means foraxially displacing said body, said differential piston forming a tubecentered on said axis and forming an outlet conduit, said differentialpiston having a net effective surface area exposed to the pressure atsaid outlet means tending to advance said control rods into said pistonsupon an increase in fluid pressure at said outlet means.

5. An axial-piston pump as defined in claim 2 wherein said control meansincludes a tubular member coaxial with said shaft and opposite thelatter, means enabling displacement of said body axially along saidtubular member, means connecting said tubular member with said chambersthrough said check valves for forming an outlet duct in said tubularmember, and an outlet port formed in said housing means andcommunicating with the interior of said tubular member,

References Cited UNITED STATES PATENTS 1,940,524 12/1933 Bellem e181.105 37 1,943,034 1/1934 Myers l03158 5 2,439,879 4/1948 Allen 103-372,524,235 10/1950 Schenk 103 -37 2,821,926 4/1958 Miller et al 103- 372,839,002 6/1958 Williams 103158 10 2,981,198 4/1961 Nettel 103 158FOREIGN PATENTS 844,436 4/1939 France. 646,371 11/1950 Great Britain.

WILLIAM L. FREEH, Primary Examiner Us. 01. X.R. 103-173

